def max():
    s = input("请输入一个小写字符串：")
    print('====================')
    su = s.upper()
    print(su)
    print('====================')

def min():
    s = input("请输入一个大写字符串：")
    print('====================')
    sl = s.lower()
    print(sl)
    print('====================')

while True:
    print("1.大写 2.小写")

    n = input("请选择：")

    if n == 1:
        max()
    else:
        min()




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